1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to sockets useful with, for example, circuit boards, and to methods of making and using the same.
2. Description of the Related Art
In various types of electronic systems, microprocessors and sometimes other types of integrated circuits are often connected to some form of larger printed circuit board, such as a motherboard, daughterboard or other type of a printed circuit board. In some cases, the integrated circuit is connected to the motherboard by direct soldering or other direct mounting techniques. In other cases, a socket is provided on the upper surface of the motherboard that is designed to receive the integrated circuit. For those integrated circuits that consist of some type of package enclosure and some plurality of conductor pins that project from the package, the motherboard socket includes a corresponding plurality of individual socket holes that are arranged spatially to match up with corresponding conductor pins on the integrated circuit package.
In one conventional socket design, the integrated circuit socket consists of a fortress-like structure that has four walls interconnected at four corners. The four walls enclose an interior space that has a bottom surface provided with a plurality of the aforementioned individual socket holes spatially arranged to receive respective conductor pins of the integrated circuit. When the integrated circuit package is seated in the socket, structural support for the integrated circuit package is provided by way of the four corners and the walls of the socket. The walls of the socket tend to be relatively narrow when compared to the length and width of the integrated circuit package. Consequently, the structural support for the integrated circuit package is largely confined to the four corners of the integrated circuit package as well as a narrow peripheral band at the edge of the integrated circuit package.
The lack of a centralized support structure for an integrated circuit package in a motherboard socket might not present a difficult problem for integrated circuits if the only downward loads associated with the integrated circuit package consisted of the weight of the package itself. However, conventional designs of integrated circuits frequently require the use of a heatsink of one form or another that is positioned and held tightly on the integrated circuit package by way of a clamping mechanism. The application of a downward clamping force on the integrated circuit package through the heatsink is resisted in the conventional design described herein by the narrow walls and corners of the socket. With little or no central support for the integrated circuit package, the application of the downward clamping force on the heatsink can result in moments acting upon the integrated circuit package substrate.
Conventional ceramic integrated circuit package substrates may have sufficient stiffness to resist the action of such moments. However, many currently-available integrated circuit packages utilize a so-called organic substrate, which consists of one or more laminated layers of polymer materials. Such polymeric substrates have greater flexibility than comparably sized ceramic substrates. Thus, an organic substrate may simply be too flexible to resist the moments associated with the heatsink clamping force. If an organic substrate undergoes excessive flexure, the central portion of the organic substrate may warp downward and produce a tensile loading and an attendant stretching of a thermal interface material interposed between the integrated circuit package lid and the enclosed integrated circuit. For those types of thermal interface materials that utilize a compliant matrix interspersed with aluminum spheres, the stretching can lead to dramatic increases in the spacing between individual aluminum spheres. As the spacing between aluminum spheres increases, the thermal conductivity of the thermal interface material may drop off and lead to temperature spiking in the integrated circuit. If the temperature spiking is severe enough, thermal shutdown may occur.
One conventional socket design does include four upwardly projecting pillars that project from the bottom surface of the socket cover to provide limited and spatially confined structural support for small areas of a microprocessor package. These pillar supports may be sufficient for specific die sizes. Another conventional design utilizes a so-called “tic tac toe” configuration. As the name implies, the tic-tac-toe configuration utilizes two sets of intersecting walls that form a tic-tac-toe pattern. The intersecting walls span the entirety of the socket floor, from one opposing wall of the socket to the other. Still another conventional design utilizes a centrally positioned mound that rises from the socket cover floor.
Conventional sockets of the type just described are often electrically and physically connected to an underlying circuit board by way of plural solder balls that are connected to corresponding contacts within the socket housing and to contact structures or pads on the circuit board. These ohmic connections are established by a reflow process that temporarily liquefies the solder balls. One pitfall of utilizing such solder structures that require a reflow is that the post reflow state of the socket housing may be warped upward slightly. Although this warpage may be relatively subtle, resulting in a height differential between the center and edge of the socket housing on the order of less than a millimeter or so, the warpage may be enough to present difficulties. One issue raised is the possibility that package designers must fabricate conductor pins with long enough lengths to compensate for the warped socket housing and still establish proper ohmic contact with the various contacts in the socket housing. Another issue is that the socket housing may not provide sufficient structural support for the central portion of the overlying socket cover and in turn the semiconductor chip package substrate that is seated thereon.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.